1. Technical Field to which the Invention Belongs
The present invention relates to a DA converter that converts a digital signal into an analog signal, and in particular to a delta sigma (hereinafter referred to as xe2x80x9cxcex94xc2x7xcexa3xe2x80x9d) type DA converter.
In addition, the present invention relates to data reproducing apparatus that utilizes the xcex94xc2x7xcexa3 type converter and reproduces an audio data of a recording medium such as a CD (compact disc).
2. Prior Art
Known DA converters include a digital circuit containing a PWM circuit, and an analog circuit that converts a PWM signal from the PWM circuit into an analog signal.
In such a DA converter, the same direct current voltage is supplied to the respective parts thereof as a power supply voltage, and the same direct current voltage drives the respective parts thereof.
However, in the existing DA converter, although a digital circuit and an analog circuit with different properties coexist, as mentioned above, both circuits are driven with the same direct current voltage. As a result, power consumption is more than necessary. Accordingly, there is a demand for reducing power consumption as a whole.
On the other hand, in order to reduce the power consumption as a whole, it is desired not to deteriorate the operational accuracy of the DA converter.
Accordingly, a first object of the present invention is to provide a DA converter that, without deteriorating the operation accuracy of the DA converter, can reduce the power consumption of a digital circuit portion thereof and as a result can reduce the power consumption as a whole.
Furthermore, a second object of the present invention is to provide a data reproducing apparatus that, without deteriorating the operation accuracy of the DA converter, can reduce the power consumption of the apparatus as a whole.
In order to overcome the above problems and to accomplish the first object, each of the respective inventions set forth below is constituted as follows.
That is, a first aspect of the invention is characterized in that in a xcex94xc2x7xcexa3 type DA converter includes a digital circuit that contains a PWM circuit; and an analog circuit that converts a PWM output value into an analog output value; wherein the xcex94xc2x7xcexa3 type converter has a first power supply that supplies a direct current voltage that is input into the analog circuit; and a second power supply that is set lower than the first power supply and supplies a direct current voltage that is input into the digital circuit; and a level shifter is interposed at an interface portion where the PWM output of the PWM circuit is input into the analog circuit, the level shifter steps up the PWM output in voltage and thereafter transfers it to the analog circuit.
Here, an operation of the invention according to the first aspect of the invention will be explained.
In a xcex94xc2x7xcexa3 type DA converter 10 shown in FIG. 1, between a PWM output of a digital circuit 5 and an analog circuit 7 that receives the PWM output, the PWM output is converted into an analog waveform that is obtained by connecting pulse heights that have values proportional to (voltagexc3x97time) of the PWM output, that is, (heightxc3x97width=area) of rectangular portions in a pulse waveform shown in FIG. 2. Accordingly, when there is a variation in the power supply of the digital circuit 5, the voltage of the PWM output, that is, a pulse height h, varies, resulting in an adverse affect on the analog circuit 7.
Now, of the (heightxc3x97width=area) of the rectangular portion in the pulse waveform of the PWM output, the pulse width, as far as there is no external noise such as jitter, has no relation with the variation of a power supply voltage VCCE. Accordingly, when a voltage corresponding to the height h (FIG. 2) of the pulse rectangular portion is stabilized or an adverse affect of the voltage variation can be eliminated, the operation accuracy of the DA converter 10 is not deteriorated.
That is, when the pulse width of the PWM output of the digital circuit is accurate, even when the pulse height h (FIG. 2) varies as the power supply of the digital circuit 5 varies, due to a voltage level-converting operation of a level shifter 11 interposed between the digital circuit 5 and the analog circuit 7 that receives the PWM output thereof, the analog circuit 7 is not adversely affected. Accordingly, the operation accuracy of the DA converter 10 is not deteriorated.
Being thus implemented, even with the power supply variation in the digital circuit 5, due to the power level-converting operation of the level shifter 11 that is interposed between the PWM output of the digital circuit 5 and the analog circuit 7 that receives the PWM output, the analog circuit 7 is not adversely affected, and the operation accuracy of the DA converter 10 is not deteriorated.
A second aspect of the invention is characterized in that, in the DA converter set forth in the first aspect of the invention, the digital circuit, the analog circuit and the level shifter are integrated on one semiconductor substrate.
A third aspect of the invention is characterized in that in a xcex94xc2x7xcexa3 type DA converter including a digital circuit containing a PWM circuit and an analog circuit that converts a PWM signal from the PWM circuit into an analog signal, in order to make an output of the analog circuit a predetermined value, the analog circuit is driven at a predetermined first direct current voltage, and the digital circuit is driven at a second direct current voltage lower than the first direct current voltage, and a level shifter is disposed at a boundary portion between the PWM circuit and the analog circuit, the level shifter steps up the PWM signal from the PWM circuit in voltage and outputs it to the analog circuit.
A fourth aspect of the invention is characterized in that, in the DA converter of the third aspect of the invention, the level shifter is driven at the first direct current voltage and the second direct current voltage.
A fifth aspect of the invention is characterized in that, in a DA converter set forth in the third or fourth aspect of the invention, the digital circuit includes a digital filter, a xcex94xc2x7xcexa3 modulator, and the PWM circuit.
A sixth aspect of the invention is characterized in that, in a DA converter set forth in any one of the third through fifth aspects of the invention, the analog circuit further includes a regulator that generates the second direct current voltage based on the first direct current voltage.
Thus, according to the respective third through sixth aspects of the invention, while noting that an analog circuit and a digital circuit have different characteristics, in order to make an output of the analog circuit a predetermined value, the analog circuit thereof is driven at a predetermined first direct current voltage and the digital circuit is driven at a second direct current voltage lower than the first direct current voltage. In addition, at a boundary portion between the PWM circuit and the analog circuit, the level shifter is interposed to step up a level of the PWM signal in voltage.
Accordingly, without deteriorating the operation accuracy of the DA converter, the power consumption of the digital circuit portion can be reduced, resulting in reducing the power consumption of the DA converter as a whole.
Next, in order to attain the second object of the present invention, each of next aspects of the invention is constituted as follows.
A seventh aspect of the invention is characterized in that a data reproducing apparatus includes; a xcex94xc2x7xcexa3 type DA converter having a first digital circuit containing a PWM circuit and an analog circuit that converts a PWM signal from the PWM circuit into an analog signal; and a second digital circuit constituted of a digital signal processing circuit that applies a predetermined digital signal process to a digital signal to be input into the xcex94xc2x7xcexa3 type DA converter; wherein in order to make an output of the analog circuit a predetermined value, the analog circuit thereof is driven at a predetermined first direct current voltage, and the first digital circuit and the second digital circuit are driven at a second direct current voltage lower than the first direct current voltage thereof; and a level shifter is interposed at a boundary portion between the PWM circuit and the analog circuit, the level shifter steps up the PWM signal from the PWM circuit in voltage and outputs it to the analog circuit.
An eighth aspect of the invention is characterized in that, in the data reproducing apparatus set forth in the seventh aspect of the invention, the level shifter is driven at the first direct current voltage and the second direct current voltage.
A ninth aspect of the invention is characterized in that, in the data reproducing apparatus set forth in the seventh or eighth aspect of the invention, the first digital circuit includes a digital filter, a xcex94xc2x7xcexa3 modulator, and the PWM circuit.
A tenth aspect of the invention is characterized in that, in the data reproducing apparatus set forth in any one of the seventh through ninth aspects of the invention, the analog circuit further includes a regulator that generates the second direct current voltage based on the first direct current voltage.
An eleventh aspect of the invention is characterized in that, in the data reproducing apparatus set forth in any one of the seventh through tenth aspects of the invention, the digital circuit, the analog circuit and the level shifter are integrated on one semiconductor substrate.
Thus, according to the respective seventh through eleventh aspects of the invention, in order to make an output of the analog circuit a predetermined value, the analog circuit thereof is driven at a predetermined first direct current voltage and the digital circuit is driven at a second direct current voltage lower than the first direct current voltage. In addition to this, at a boundary portion between the PWM circuit and the analog circuit, the level shifter is interposed to step up a voltage level of the PWM signal outputted from the PWM circuit and to output it to the analog circuit.
Accordingly, the operation accuracy of the xcex94xc2x7xcexa3 type DA converter is not deteriorated, and moreover, the power consumption of the digital circuit portion including the digital signal processing circuit preceding the DA conversion can be reduced, resulting in reducing the power consumption of the apparatus as a whole.